The invention relates to a process for braking a vehicle as well as to braking systems for carrying out the process. Hereinafter, the terms "front axle brake" and "rear axle brake" will be used to refer collectively to all the components participating in producing the braking force in the area of the appertaining axle group.
In designing a braking system and the brake pressure distribution between the axle groups, the criteria for "equal adhesion utilization (.mu.) between all the wheels and the road surface" and "equally great brake lining wear on all brakes" play important roles. The advantage of "equal adhesion utilization (.mu.)" consists of optimal braking with good directional stability of the vehicle during braking. A braking system offering such a utilization of adhesion can be said to be "stability-optimized" in braking. A braking system with "equally great brake lining wear on all brakes" can be said to be "wear-optimized." As a result of wear optimization, all of the vehicle's brake linings can be replaced at the same time and this criterion thus offers economic advantages.
If the arrangement of the brake components is established, the brake pressure distribution among the axles determines for a given vehicle mass whether the braking system is operated in a stability-optimized mode, a wear optimized mode, or some other mode.
FIGS. 1 and 2 show schematic ideal curves for the front axle brake pressure p.sub.1 and for the rear axle brake pressure p.sub.2 as functions of vehicle deceleration command signals for stability-optimized operation of the braking system with different vehicle masses and for wear-optimized operation that is always independent of load. These curves can be calculated in a known manner by using characteristic data of the brake components as well as the load data and certain dimensions of the vehicle.
The curve for wear-optimized operation shown here is based according to the invention on the condition of equal specific brake lining load, i.e., equal surface pressure or energy per surface unit on all brakes. The curves for wear-optimized operation are straight lines, while the ideal curves for stability-optimized operation are parabolas shown in dashed line. The different characteristics of the curves in FIGS. 1 and 2 show that it is impossible to design a braking system so as to be simultaneously wear-optimized and stability-optimized.
It is known that in practical vehicle operation, most of the braking is done within a partial braking range for small vehicle deceleration (i.e., up to approx. 0.3 g), and with correspondingly low brake pressures. As a result, the brake lining wear occurs mainly owing to low brake pressures.
A process for distributing the braking pressure between a front axle brake group and a rear axle brake group is known from DE 35 02 051 A1, in particular from page 10, last paragraph therein. In the process described therein, it was suggested to provide for brake pressure distribution within the partial range, i.e., in the presence of lower deceleration command signals, in a wear-optimized manner and to change over to a stability-optimized mode in the presence of greater deceleration command signals. However, as a consequence of the jump that is involved between the curves, a sudden change in brake pressure and thereby a sudden change in vehicle deceleration (i.e., a jolt) cannot be avoided.
It is the object of the instant invention to further develop a process for distributing the braking pressure between the front axle brake group and the rear axle brake group by simple means and in such a manner as to ensure a non-sudden evolution of brake pressure and a non-sudden (i.e., jolt-free) evolution of vehicle deceleration.